4. possibly, with certain devices and bootloaders.
In some cases, the bootloader version can affect USB transfer speeds.
Should I always update my bootloader when I find a newer one?
No! Leave the bootloader as is. No need to upgrade it and you gain nothing by upgrading it.
Is a certain bootloader recommended for a certain device?
Yes. For your ONE model, 5.5128 and 5.5136 are recommended, but not absolutely necessary.
IMPORTANT: You can brick your device by experimenting with different bootloaders, therefore it is NOT recommended to change your bootloader. Don't say I didn't warn you
Google "tomtom bootloader" for more info.